[deliverable/linux.git] / net / ipv4 / tcp_compound.c

/*
 * TCP Vegas congestion control
 *
 * This is based on the congestion detection/avoidance scheme described in
 *    Lawrence S. Brakmo and Larry L. Peterson.
 *    "TCP Vegas: End to end congestion avoidance on a global internet."
 *    IEEE Journal on Selected Areas in Communication, 13(8):1465--1480,
 *    October 1995. Available from:
 *	ftp://ftp.cs.arizona.edu/xkernel/Papers/jsac.ps
 *
 * See http://www.cs.arizona.edu/xkernel/ for their implementation.
 * The main aspects that distinguish this implementation from the
 * Arizona Vegas implementation are:
 *   o We do not change the loss detection or recovery mechanisms of
 *     Linux in any way. Linux already recovers from losses quite well,
 *     using fine-grained timers, NewReno, and FACK.
 *   o To avoid the performance penalty imposed by increasing cwnd
 *     only every-other RTT during slow start, we increase during
 *     every RTT during slow start, just like Reno.
 *   o Largely to allow continuous cwnd growth during slow start,
 *     we use the rate at which ACKs come back as the "actual"
 *     rate, rather than the rate at which data is sent.
 *   o To speed convergence to the right rate, we set the cwnd
 *     to achieve the right ("actual") rate when we exit slow start.
 *   o To filter out the noise caused by delayed ACKs, we use the
 *     minimum RTT sample observed during the last RTT to calculate
 *     the actual rate.
 *   o When the sender re-starts from idle, it waits until it has
 *     received ACKs for an entire flight of new data before making
 *     a cwnd adjustment decision. The original Vegas implementation
 *     assumed senders never went idle.
 *
 *
 *   TCP Compound based on TCP Vegas
 *
 *   further details can be found here:
 *      ftp://ftp.research.microsoft.com/pub/tr/TR-2005-86.pdf
 */

#include <linux/config.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/inet_diag.h>

#include <net/tcp.h>

/* Default values of the Vegas variables, in fixed-point representation
 * with V_PARAM_SHIFT bits to the right of the binary point.
 */
#define V_PARAM_SHIFT 1

#define TCP_COMPOUND_ALPHA          3U
#define TCP_COMPOUND_BETA           1U
#define TCP_COMPOUND_GAMMA         30
#define TCP_COMPOUND_ZETA           1

/* TCP compound variables */
struct compound {
	u32 beg_snd_nxt;	/* right edge during last RTT */
	u32 beg_snd_una;	/* left edge  during last RTT */
	u32 beg_snd_cwnd;	/* saves the size of the cwnd */
	u8 doing_vegas_now;	/* if true, do vegas for this RTT */
	u16 cntRTT;		/* # of RTTs measured within last RTT */
	u32 minRTT;		/* min of RTTs measured within last RTT (in usec) */
	u32 baseRTT;		/* the min of all Vegas RTT measurements seen (in usec) */

	u32 cwnd;
	u32 dwnd;
};

/* There are several situations when we must "re-start" Vegas:
 *
 *  o when a connection is established
 *  o after an RTO
 *  o after fast recovery
 *  o when we send a packet and there is no outstanding
 *    unacknowledged data (restarting an idle connection)
 *
 * In these circumstances we cannot do a Vegas calculation at the
 * end of the first RTT, because any calculation we do is using
 * stale info -- both the saved cwnd and congestion feedback are
 * stale.
 *
 * Instead we must wait until the completion of an RTT during
 * which we actually receive ACKs.
 */
static inline void vegas_enable(struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	struct compound *vegas = inet_csk_ca(sk);

	/* Begin taking Vegas samples next time we send something. */
	vegas->doing_vegas_now = 1;

	/* Set the beginning of the next send window. */
	vegas->beg_snd_nxt = tp->snd_nxt;

	vegas->cntRTT = 0;
	vegas->minRTT = 0x7fffffff;
}

/* Stop taking Vegas samples for now. */
static inline void vegas_disable(struct sock *sk)
{
	struct compound *vegas = inet_csk_ca(sk);

	vegas->doing_vegas_now = 0;
}

static void tcp_compound_init(struct sock *sk)
{
	struct compound *vegas = inet_csk_ca(sk);
	const struct tcp_sock *tp = tcp_sk(sk);

	vegas->baseRTT = 0x7fffffff;
	vegas_enable(sk);

	vegas->dwnd = 0;
	vegas->cwnd = tp->snd_cwnd;
}

/* Do RTT sampling needed for Vegas.
 * Basically we:
 *   o min-filter RTT samples from within an RTT to get the current
 *     propagation delay + queuing delay (we are min-filtering to try to
 *     avoid the effects of delayed ACKs)
 *   o min-filter RTT samples from a much longer window (forever for now)
 *     to find the propagation delay (baseRTT)
 */
static void tcp_compound_rtt_calc(struct sock *sk, u32 usrtt)
{
	struct compound *vegas = inet_csk_ca(sk);
	u32 vrtt = usrtt + 1;	/* Never allow zero rtt or baseRTT */

	/* Filter to find propagation delay: */
	if (vrtt < vegas->baseRTT)
		vegas->baseRTT = vrtt;

	/* Find the min RTT during the last RTT to find
	 * the current prop. delay + queuing delay:
	 */

	vegas->minRTT = min(vegas->minRTT, vrtt);
	vegas->cntRTT++;
}

static void tcp_compound_state(struct sock *sk, u8 ca_state)
{

	if (ca_state == TCP_CA_Open)
		vegas_enable(sk);
	else
		vegas_disable(sk);
}


/* 64bit divisor, dividend and result. dynamic precision */
static inline u64 div64_64(u64 dividend, u64 divisor)
{
	u32 d = divisor;

	if (divisor > 0xffffffffULL) {
		unsigned int shift = fls(divisor >> 32);

		d = divisor >> shift;
		dividend >>= shift;
	}

	/* avoid 64 bit division if possible */
	if (dividend >> 32)
		do_div(dividend, d);
	else
		dividend = (u32) dividend / d;

	return dividend;
}

/* calculate the quartic root of "a" using Newton-Raphson */
static u32 qroot(u64 a)
{
	u32 x, x1;

	/* Initial estimate is based on:
	 * qrt(x) = exp(log(x) / 4)
	 */
	x = 1u << (fls64(a) >> 2);

	/*
	 * Iteration based on:
	 *                         3
	 * x    = ( 3 * x  +  a / x  ) / 4
	 *  k+1          k         k
	 */
	do {
		u64 x3 = x;

		x1 = x;
		x3 *= x;
		x3 *= x;

		x = (3 * x + (u32) div64_64(a, x3)) / 4;
	} while (abs(x1 - x) > 1);

	return x;
}


/*
 * If the connection is idle and we are restarting,
 * then we don't want to do any Vegas calculations
 * until we get fresh RTT samples.  So when we
 * restart, we reset our Vegas state to a clean
 * slate. After we get acks for this flight of
 * packets, _then_ we can make Vegas calculations
 * again.
 */
static void tcp_compound_cwnd_event(struct sock *sk, enum tcp_ca_event event)
{
	if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START)
		tcp_compound_init(sk);
}

static void tcp_compound_cong_avoid(struct sock *sk, u32 ack,
				    u32 seq_rtt, u32 in_flight, int flag)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct compound *vegas = inet_csk_ca(sk);
	u8 inc = 0;

	if (vegas->cwnd + vegas->dwnd > tp->snd_cwnd) {
		if (vegas->cwnd > tp->snd_cwnd || vegas->dwnd > tp->snd_cwnd) {
			vegas->cwnd = tp->snd_cwnd;
			vegas->dwnd = 0;
		} else
			vegas->cwnd = tp->snd_cwnd - vegas->dwnd;

	}

	if (!tcp_is_cwnd_limited(sk, in_flight))
		return;

	if (vegas->cwnd <= tp->snd_ssthresh)
		inc = 1;
	else if (tp->snd_cwnd_cnt < tp->snd_cwnd)
		tp->snd_cwnd_cnt++;

	if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
		inc = 1;
		tp->snd_cwnd_cnt = 0;
	}

	if (inc && tp->snd_cwnd < tp->snd_cwnd_clamp)
		vegas->cwnd++;

	/* The key players are v_beg_snd_una and v_beg_snd_nxt.
	 *
	 * These are so named because they represent the approximate values
	 * of snd_una and snd_nxt at the beginning of the current RTT. More
	 * precisely, they represent the amount of data sent during the RTT.
	 * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
	 * we will calculate that (v_beg_snd_nxt - v_beg_snd_una) outstanding
	 * bytes of data have been ACKed during the course of the RTT, giving
	 * an "actual" rate of:
	 *
	 *     (v_beg_snd_nxt - v_beg_snd_una) / (rtt duration)
	 *
	 * Unfortunately, v_beg_snd_una is not exactly equal to snd_una,
	 * because delayed ACKs can cover more than one segment, so they
	 * don't line up nicely with the boundaries of RTTs.
	 *
	 * Another unfortunate fact of life is that delayed ACKs delay the
	 * advance of the left edge of our send window, so that the number
	 * of bytes we send in an RTT is often less than our cwnd will allow.
	 * So we keep track of our cwnd separately, in v_beg_snd_cwnd.
	 */

	if (after(ack, vegas->beg_snd_nxt)) {
		/* Do the Vegas once-per-RTT cwnd adjustment. */
		u32 old_wnd, old_snd_cwnd;

		/* Here old_wnd is essentially the window of data that was
		 * sent during the previous RTT, and has all
		 * been acknowledged in the course of the RTT that ended
		 * with the ACK we just received. Likewise, old_snd_cwnd
		 * is the cwnd during the previous RTT.
		 */
		if (!tp->mss_cache)
			return;

		old_wnd = (vegas->beg_snd_nxt - vegas->beg_snd_una) /
		    tp->mss_cache;
		old_snd_cwnd = vegas->beg_snd_cwnd;

		/* Save the extent of the current window so we can use this
		 * at the end of the next RTT.
		 */
		vegas->beg_snd_una = vegas->beg_snd_nxt;
		vegas->beg_snd_nxt = tp->snd_nxt;
		vegas->beg_snd_cwnd = tp->snd_cwnd;

		/* We do the Vegas calculations only if we got enough RTT
		 * samples that we can be reasonably sure that we got
		 * at least one RTT sample that wasn't from a delayed ACK.
		 * If we only had 2 samples total,
		 * then that means we're getting only 1 ACK per RTT, which
		 * means they're almost certainly delayed ACKs.
		 * If  we have 3 samples, we should be OK.
		 */

		if (vegas->cntRTT > 2) {
			u32 rtt, target_cwnd, diff;
			u32 brtt, dwnd;

			/* We have enough RTT samples, so, using the Vegas
			 * algorithm, we determine if we should increase or
			 * decrease cwnd, and by how much.
			 */

			/* Pluck out the RTT we are using for the Vegas
			 * calculations. This is the min RTT seen during the
			 * last RTT. Taking the min filters out the effects
			 * of delayed ACKs, at the cost of noticing congestion
			 * a bit later.
			 */
			rtt = vegas->minRTT;

			/* Calculate the cwnd we should have, if we weren't
			 * going too fast.
			 *
			 * This is:
			 *     (actual rate in segments) * baseRTT
			 * We keep it as a fixed point number with
			 * V_PARAM_SHIFT bits to the right of the binary point.
			 */
			if (!rtt)
				return;

			brtt = vegas->baseRTT;
			target_cwnd = ((old_wnd * brtt)
				       << V_PARAM_SHIFT) / rtt;

			/* Calculate the difference between the window we had,
			 * and the window we would like to have. This quantity
			 * is the "Diff" from the Arizona Vegas papers.
			 *
			 * Again, this is a fixed point number with
			 * V_PARAM_SHIFT bits to the right of the binary
			 * point.
			 */

			diff = (old_wnd << V_PARAM_SHIFT) - target_cwnd;

			dwnd = vegas->dwnd;

			if (diff < (TCP_COMPOUND_GAMMA << V_PARAM_SHIFT)) {
				u64 v;
				u32 x;

				/*
				 * The TCP Compound paper describes the choice
				 * of "k" determines the agressiveness,
				 * ie. slope of the response function.
				 *
				 * For same value as HSTCP would be 0.8
				 * but for computaional reasons, both the
				 * original authors and this implementation
				 * use 0.75.
				 */
				v = old_wnd;
				x = qroot(v * v * v) >> TCP_COMPOUND_ALPHA;
				if (x > 1)
					dwnd = x - 1;
				else
					dwnd = 0;

				dwnd += vegas->dwnd;

			} else if ((dwnd << V_PARAM_SHIFT) <
				   (diff * TCP_COMPOUND_BETA))
				dwnd = 0;
			else
				dwnd =
				    ((dwnd << V_PARAM_SHIFT) -
				     (diff *
				      TCP_COMPOUND_BETA)) >> V_PARAM_SHIFT;

			vegas->dwnd = dwnd;

		}

		/* Wipe the slate clean for the next RTT. */
		vegas->cntRTT = 0;
		vegas->minRTT = 0x7fffffff;
	}

	tp->snd_cwnd = vegas->cwnd + vegas->dwnd;
}

/* Extract info for Tcp socket info provided via netlink. */
static void tcp_compound_get_info(struct sock *sk, u32 ext, struct sk_buff *skb)
{
	const struct compound *ca = inet_csk_ca(sk);
	if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
		struct tcpvegas_info *info;

		info = RTA_DATA(__RTA_PUT(skb, INET_DIAG_VEGASINFO,
					  sizeof(*info)));

		info->tcpv_enabled = ca->doing_vegas_now;
		info->tcpv_rttcnt = ca->cntRTT;
		info->tcpv_rtt = ca->baseRTT;
		info->tcpv_minrtt = ca->minRTT;
	rtattr_failure:;
	}
}

static struct tcp_congestion_ops tcp_compound = {
	.init		= tcp_compound_init,
	.ssthresh	= tcp_reno_ssthresh,
	.cong_avoid	= tcp_compound_cong_avoid,
	.min_cwnd	= tcp_reno_min_cwnd,
	.rtt_sample	= tcp_compound_rtt_calc,
	.set_state	= tcp_compound_state,
	.cwnd_event	= tcp_compound_cwnd_event,
	.get_info	= tcp_compound_get_info,

	.owner		= THIS_MODULE,
	.name		= "compound",
};

static int __init tcp_compound_register(void)
{
	BUG_ON(sizeof(struct compound) > ICSK_CA_PRIV_SIZE);
	tcp_register_congestion_control(&tcp_compound);
	return 0;
}

static void __exit tcp_compound_unregister(void)
{
	tcp_unregister_congestion_control(&tcp_compound);
}

module_init(tcp_compound_register);
module_exit(tcp_compound_unregister);

MODULE_AUTHOR("Angelo P. Castellani, Stephen Hemminger");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("TCP Compound");
Commit	Line	Data
f890f921 AC	1	/*
	2	* TCP Vegas congestion control
	3	*
	4	* This is based on the congestion detection/avoidance scheme described in
	5	* Lawrence S. Brakmo and Larry L. Peterson.
	6	* "TCP Vegas: End to end congestion avoidance on a global internet."
	7	* IEEE Journal on Selected Areas in Communication, 13(8):1465--1480,
	8	* October 1995. Available from:
	9	* ftp://ftp.cs.arizona.edu/xkernel/Papers/jsac.ps
	10	*
	11	* See http://www.cs.arizona.edu/xkernel/ for their implementation.
	12	* The main aspects that distinguish this implementation from the
	13	* Arizona Vegas implementation are:
	14	* o We do not change the loss detection or recovery mechanisms of
	15	* Linux in any way. Linux already recovers from losses quite well,
	16	* using fine-grained timers, NewReno, and FACK.
	17	* o To avoid the performance penalty imposed by increasing cwnd
	18	* only every-other RTT during slow start, we increase during
	19	* every RTT during slow start, just like Reno.
	20	* o Largely to allow continuous cwnd growth during slow start,
	21	* we use the rate at which ACKs come back as the "actual"
	22	* rate, rather than the rate at which data is sent.
	23	* o To speed convergence to the right rate, we set the cwnd
	24	* to achieve the right ("actual") rate when we exit slow start.
	25	* o To filter out the noise caused by delayed ACKs, we use the
	26	* minimum RTT sample observed during the last RTT to calculate
	27	* the actual rate.
	28	* o When the sender re-starts from idle, it waits until it has
	29	* received ACKs for an entire flight of new data before making
	30	* a cwnd adjustment decision. The original Vegas implementation
	31	* assumed senders never went idle.
	32	*
	33	*
	34	* TCP Compound based on TCP Vegas
	35	*
	36	* further details can be found here:
	37	* ftp://ftp.research.microsoft.com/pub/tr/TR-2005-86.pdf
	38	*/
	39
	40	#include <linux/config.h>
	41	#include <linux/mm.h>
	42	#include <linux/module.h>
	43	#include <linux/skbuff.h>
	44	#include <linux/inet_diag.h>
	45
	46	#include <net/tcp.h>
	47
	48	/* Default values of the Vegas variables, in fixed-point representation
	49	* with V_PARAM_SHIFT bits to the right of the binary point.
	50	*/
	51	#define V_PARAM_SHIFT 1
	52
	53	#define TCP_COMPOUND_ALPHA 3U
	54	#define TCP_COMPOUND_BETA 1U
f890f921 AC	55	#define TCP_COMPOUND_GAMMA 30
	56	#define TCP_COMPOUND_ZETA 1
	57
	58	/* TCP compound variables */
	59	struct compound {
	60	u32 beg_snd_nxt; /* right edge during last RTT */
	61	u32 beg_snd_una; /* left edge during last RTT */
	62	u32 beg_snd_cwnd; /* saves the size of the cwnd */
	63	u8 doing_vegas_now; /* if true, do vegas for this RTT */
	64	u16 cntRTT; /* # of RTTs measured within last RTT */
	65	u32 minRTT; /* min of RTTs measured within last RTT (in usec) */
	66	u32 baseRTT; /* the min of all Vegas RTT measurements seen (in usec) */
	67
	68	u32 cwnd;
	69	u32 dwnd;
	70	};
	71
	72	/* There are several situations when we must "re-start" Vegas:
	73	*
	74	* o when a connection is established
	75	* o after an RTO
	76	* o after fast recovery
	77	* o when we send a packet and there is no outstanding
	78	* unacknowledged data (restarting an idle connection)
	79	*
	80	* In these circumstances we cannot do a Vegas calculation at the
	81	* end of the first RTT, because any calculation we do is using
	82	* stale info -- both the saved cwnd and congestion feedback are
	83	* stale.
	84	*
	85	* Instead we must wait until the completion of an RTT during
	86	* which we actually receive ACKs.
	87	*/
	88	static inline void vegas_enable(struct sock *sk)
	89	{
	90	const struct tcp_sock *tp = tcp_sk(sk);
	91	struct compound *vegas = inet_csk_ca(sk);
	92
	93	/* Begin taking Vegas samples next time we send something. */
	94	vegas->doing_vegas_now = 1;
	95
	96	/* Set the beginning of the next send window. */
	97	vegas->beg_snd_nxt = tp->snd_nxt;
	98
	99	vegas->cntRTT = 0;
	100	vegas->minRTT = 0x7fffffff;
	101	}
	102
	103	/* Stop taking Vegas samples for now. */
	104	static inline void vegas_disable(struct sock *sk)
	105	{
	106	struct compound *vegas = inet_csk_ca(sk);
	107
	108	vegas->doing_vegas_now = 0;
	109	}
	110
	111	static void tcp_compound_init(struct sock *sk)
	112	{
	113	struct compound *vegas = inet_csk_ca(sk);
	114	const struct tcp_sock *tp = tcp_sk(sk);
	115
	116	vegas->baseRTT = 0x7fffffff;
	117	vegas_enable(sk);
	118
119	vegas->dwnd = 0;
120	vegas->cwnd = tp->snd_cwnd;
121	}
122
123	/* Do RTT sampling needed for Vegas.
124	* Basically we:
125	* o min-filter RTT samples from within an RTT to get the current
126	* propagation delay + queuing delay (we are min-filtering to try to
127	* avoid the effects of delayed ACKs)
128	* o min-filter RTT samples from a much longer window (forever for now)
129	* to find the propagation delay (baseRTT)
130	*/
131	static void tcp_compound_rtt_calc(struct sock *sk, u32 usrtt)
132	{
133	struct compound *vegas = inet_csk_ca(sk);
134	u32 vrtt = usrtt + 1; /* Never allow zero rtt or baseRTT */
135
136	/* Filter to find propagation delay: */
137	if (vrtt < vegas->baseRTT)
138	vegas->baseRTT = vrtt;
139
140	/* Find the min RTT during the last RTT to find
141	* the current prop. delay + queuing delay:
142	*/
143
144	vegas->minRTT = min(vegas->minRTT, vrtt);
145	vegas->cntRTT++;
146	}
147
148	static void tcp_compound_state(struct sock *sk, u8 ca_state)
149	{
150
151	if (ca_state == TCP_CA_Open)
152	vegas_enable(sk);
153	else
154	vegas_disable(sk);
155	}
156
a4ed2584 SH	157
	158	/* 64bit divisor, dividend and result. dynamic precision */
	159	static inline u64 div64_64(u64 dividend, u64 divisor)
	160	{
	161	u32 d = divisor;
	162
	163	if (divisor > 0xffffffffULL) {
	164	unsigned int shift = fls(divisor >> 32);
	165
	166	d = divisor >> shift;
	167	dividend >>= shift;
	168	}
	169
	170	/* avoid 64 bit division if possible */
	171	if (dividend >> 32)
	172	do_div(dividend, d);
	173	else
	174	dividend = (u32) dividend / d;
	175
	176	return dividend;
	177	}
	178
	179	/* calculate the quartic root of "a" using Newton-Raphson */
	180	static u32 qroot(u64 a)
	181	{
	182	u32 x, x1;
	183
	184	/* Initial estimate is based on:
	185	* qrt(x) = exp(log(x) / 4)
	186	*/
	187	x = 1u << (fls64(a) >> 2);
	188
	189	/*
	190	* Iteration based on:
	191	* 3
	192	* x = ( 3 * x + a / x ) / 4
	193	* k+1 k k
	194	*/
	195	do {
	196	u64 x3 = x;
	197
	198	x1 = x;
	199	x3 *= x;
	200	x3 *= x;
	201
	202	x = (3 * x + (u32) div64_64(a, x3)) / 4;
	203	} while (abs(x1 - x) > 1);
	204
	205	return x;
	206	}
	207
	208
f890f921 AC	209	/*
	210	* If the connection is idle and we are restarting,
	211	* then we don't want to do any Vegas calculations
	212	* until we get fresh RTT samples. So when we
	213	* restart, we reset our Vegas state to a clean
	214	* slate. After we get acks for this flight of
	215	* packets, _then_ we can make Vegas calculations
	216	* again.
	217	*/
	218	static void tcp_compound_cwnd_event(struct sock *sk, enum tcp_ca_event event)
	219	{
	220	if (event == CA_EVENT_CWND_RESTART \|\| event == CA_EVENT_TX_START)
	221	tcp_compound_init(sk);
	222	}
	223
	224	static void tcp_compound_cong_avoid(struct sock *sk, u32 ack,
	225	u32 seq_rtt, u32 in_flight, int flag)
	226	{
	227	struct tcp_sock *tp = tcp_sk(sk);
	228	struct compound *vegas = inet_csk_ca(sk);
	229	u8 inc = 0;
	230
	231	if (vegas->cwnd + vegas->dwnd > tp->snd_cwnd) {
	232	if (vegas->cwnd > tp->snd_cwnd \|\| vegas->dwnd > tp->snd_cwnd) {
	233	vegas->cwnd = tp->snd_cwnd;
	234	vegas->dwnd = 0;
	235	} else
	236	vegas->cwnd = tp->snd_cwnd - vegas->dwnd;
	237
	238	}
	239
	240	if (!tcp_is_cwnd_limited(sk, in_flight))
	241	return;
	242
	243	if (vegas->cwnd <= tp->snd_ssthresh)
	244	inc = 1;
	245	else if (tp->snd_cwnd_cnt < tp->snd_cwnd)
	246	tp->snd_cwnd_cnt++;
	247
	248	if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
	249	inc = 1;
	250	tp->snd_cwnd_cnt = 0;
	251	}
	252
	253	if (inc && tp->snd_cwnd < tp->snd_cwnd_clamp)
	254	vegas->cwnd++;
	255
	256	/* The key players are v_beg_snd_una and v_beg_snd_nxt.
	257	*
	258	* These are so named because they represent the approximate values
	259	* of snd_una and snd_nxt at the beginning of the current RTT. More
	260	* precisely, they represent the amount of data sent during the RTT.
	261	* At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
	262	* we will calculate that (v_beg_snd_nxt - v_beg_snd_una) outstanding
	263	* bytes of data have been ACKed during the course of the RTT, giving
	264	* an "actual" rate of:
	265	*
	266	* (v_beg_snd_nxt - v_beg_snd_una) / (rtt duration)
	267	*
	268	* Unfortunately, v_beg_snd_una is not exactly equal to snd_una,
	269	* because delayed ACKs can cover more than one segment, so they
	270	* don't line up nicely with the boundaries of RTTs.
	271	*
	272	* Another unfortunate fact of life is that delayed ACKs delay the
273	* advance of the left edge of our send window, so that the number
274	* of bytes we send in an RTT is often less than our cwnd will allow.
275	* So we keep track of our cwnd separately, in v_beg_snd_cwnd.
276	*/
277
278	if (after(ack, vegas->beg_snd_nxt)) {
279	/* Do the Vegas once-per-RTT cwnd adjustment. */
280	u32 old_wnd, old_snd_cwnd;
281
282	/* Here old_wnd is essentially the window of data that was
283	* sent during the previous RTT, and has all
284	* been acknowledged in the course of the RTT that ended
285	* with the ACK we just received. Likewise, old_snd_cwnd
286	* is the cwnd during the previous RTT.
287	*/
288	if (!tp->mss_cache)
289	return;
290
291	old_wnd = (vegas->beg_snd_nxt - vegas->beg_snd_una) /
292	tp->mss_cache;
293	old_snd_cwnd = vegas->beg_snd_cwnd;
294
295	/* Save the extent of the current window so we can use this
296	* at the end of the next RTT.
297	*/
298	vegas->beg_snd_una = vegas->beg_snd_nxt;
299	vegas->beg_snd_nxt = tp->snd_nxt;
300	vegas->beg_snd_cwnd = tp->snd_cwnd;
301
302	/* We do the Vegas calculations only if we got enough RTT
303	* samples that we can be reasonably sure that we got
304	* at least one RTT sample that wasn't from a delayed ACK.
305	* If we only had 2 samples total,
306	* then that means we're getting only 1 ACK per RTT, which
307	* means they're almost certainly delayed ACKs.
308	* If we have 3 samples, we should be OK.
309	*/
310
311	if (vegas->cntRTT > 2) {
312	u32 rtt, target_cwnd, diff;
313	u32 brtt, dwnd;
314
315	/* We have enough RTT samples, so, using the Vegas
316	* algorithm, we determine if we should increase or
317	* decrease cwnd, and by how much.
318	*/
319
320	/* Pluck out the RTT we are using for the Vegas
321	* calculations. This is the min RTT seen during the
322	* last RTT. Taking the min filters out the effects
323	* of delayed ACKs, at the cost of noticing congestion
324	* a bit later.
325	*/
326	rtt = vegas->minRTT;
327
328	/* Calculate the cwnd we should have, if we weren't
329	* going too fast.
330	*
331	* This is:
332	* (actual rate in segments) * baseRTT
333	* We keep it as a fixed point number with
334	* V_PARAM_SHIFT bits to the right of the binary point.
335	*/
336	if (!rtt)
337	return;
338
339	brtt = vegas->baseRTT;
340	target_cwnd = ((old_wnd * brtt)
341	<< V_PARAM_SHIFT) / rtt;
342
343	/* Calculate the difference between the window we had,
344	* and the window we would like to have. This quantity
345	* is the "Diff" from the Arizona Vegas papers.
346	*
347	* Again, this is a fixed point number with
348	* V_PARAM_SHIFT bits to the right of the binary
349	* point.
350	*/
351
352	diff = (old_wnd << V_PARAM_SHIFT) - target_cwnd;
353
354	dwnd = vegas->dwnd;
355
356	if (diff < (TCP_COMPOUND_GAMMA << V_PARAM_SHIFT)) {
f890f921	357	u64 v;
a4ed2584 SH	358	u32 x;
	359
	360	/*
	361	* The TCP Compound paper describes the choice
	362	* of "k" determines the agressiveness,
	363	* ie. slope of the response function.
	364	*
	365	* For same value as HSTCP would be 0.8
	366	* but for computaional reasons, both the
	367	* original authors and this implementation
	368	* use 0.75.
	369	*/
	370	v = old_wnd;
	371	x = qroot(v * v * v) >> TCP_COMPOUND_ALPHA;
f890f921 AC	372	if (x > 1)
	373	dwnd = x - 1;
	374	else
	375	dwnd = 0;
	376
	377	dwnd += vegas->dwnd;
	378
	379	} else if ((dwnd << V_PARAM_SHIFT) <
	380	(diff * TCP_COMPOUND_BETA))
	381	dwnd = 0;
	382	else
	383	dwnd =
	384	((dwnd << V_PARAM_SHIFT) -
	385	(diff *
	386	TCP_COMPOUND_BETA)) >> V_PARAM_SHIFT;
	387
	388	vegas->dwnd = dwnd;
	389
	390	}
	391
	392	/* Wipe the slate clean for the next RTT. */
	393	vegas->cntRTT = 0;
	394	vegas->minRTT = 0x7fffffff;
	395	}
	396
	397	tp->snd_cwnd = vegas->cwnd + vegas->dwnd;
	398	}
	399
	400	/* Extract info for Tcp socket info provided via netlink. */
	401	static void tcp_compound_get_info(struct sock sk, u32 ext, struct sk_buff skb)
	402	{
	403	const struct compound *ca = inet_csk_ca(sk);
	404	if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
	405	struct tcpvegas_info *info;
	406
	407	info = RTA_DATA(__RTA_PUT(skb, INET_DIAG_VEGASINFO,
	408	sizeof(*info)));
	409
	410	info->tcpv_enabled = ca->doing_vegas_now;
	411	info->tcpv_rttcnt = ca->cntRTT;
	412	info->tcpv_rtt = ca->baseRTT;
	413	info->tcpv_minrtt = ca->minRTT;
	414	rtattr_failure:;
	415	}
	416	}
	417
	418	static struct tcp_congestion_ops tcp_compound = {
	419	.init = tcp_compound_init,
	420	.ssthresh = tcp_reno_ssthresh,
	421	.cong_avoid = tcp_compound_cong_avoid,
	422	.min_cwnd = tcp_reno_min_cwnd,
	423	.rtt_sample = tcp_compound_rtt_calc,
	424	.set_state = tcp_compound_state,
	425	.cwnd_event = tcp_compound_cwnd_event,
	426	.get_info = tcp_compound_get_info,
	427
	428	.owner = THIS_MODULE,
	429	.name = "compound",
	430	};
	431
	432	static int __init tcp_compound_register(void)
	433	{
	434	BUG_ON(sizeof(struct compound) > ICSK_CA_PRIV_SIZE);
	435	tcp_register_congestion_control(&tcp_compound);
436	return 0;
437	}
438
439	static void __exit tcp_compound_unregister(void)
440	{
441	tcp_unregister_congestion_control(&tcp_compound);
442	}
443
444	module_init(tcp_compound_register);
445	module_exit(tcp_compound_unregister);
446
447	MODULE_AUTHOR("Angelo P. Castellani, Stephen Hemminger");
448	MODULE_LICENSE("GPL");
449	MODULE_DESCRIPTION("TCP Compound");